Chemical process



CHEMICAL PROCESS 10 Claims. (Cl. 260-609) This invention relates toimprovements in the free radical catalyzed reaction of hydrogen sulfidewith hydro- This application is a continuation-in-part of our Serial No.

568,200, filed February 28, 1956, now abandoned.

The reaction of hydrogen sulfide with hydrocarbons containing anolefinic linkage in the presence of free tans directly, the poor yieldsand the production of byproducts has been such that manufacturers haveresorted to indirect synthesis routes, e. g. the synthesis of primarymercaptans from chlorinated hydrocarbons.

An ob ect of this invention is to provide a method for obtaining fasterreaction rates and more complete con- Patented-Dec; 23, 1958 .Any of thefree radical catalytic agents heretofore used in catalyzing the reactionbetween hydrogen sulfide and hydrocarbons having an olefinic linkage maybe used in the practice of this invention. For example, peroxidecompounds, organic azo compounds, ultraviolet radiations of below 3,000Angstrom units, etc. can be employed. While di-tertiaryalkyl peroxidessuch as di-tertiarybutyl peroxides are highly effective free radicalcatalysts for this reaction,the other dialkyl peroxides, alkyl hydroperoxides, alkyl peroxy. esters, diacyl peroxides, which are effectivecatalysts, for this reaction may be utilized. The peroxide free'radicalcatalysts are, of course, employed at temperatures at which the peroxidedecomposes to form free radicals, the particular optimum temperatureused varying to some extent with the different peroxides employed. Forexample, with di-tertiarybutyl peroxide, reaction temperatures of from100 to 150 C. or thereabouts, e; g. 125 C., with pressures of 100-2500p. s. i. g. and reaction times of 0.5 to hours can be employed. Likewisethe various azo catalysts which cause this reaction to occur via a freeradical mechanism may be used. For instance the azo catalysts which havean acyclic azo group, N=N, bonded to different non-aromatics, i. e.aliphaticor cycloaliphatic carbons, at least one of which 5 is tertiarycan be used. Such compounds and their use for catalyzing the freeradical addition of hydrogen sulfide to olefinic linkages is describedin U. S. 2,551,813. As an example, alpha,alpha'-azodiisobutyronitrilecan be used in catalyzing the free radical reaction of hydrogen sulfidewith an olefinic hydrocarbon, and when water is added to the reactionzone (which may conveniently be maintained at a temperature of 40-150"0., while using reaction times of from .1 to 24 hours and pressures oftive for producing mercaptan compounds in preference to organicsulfides. A further object is to provide a process for producing prlmarymercaptans from alpha-olefins and vantages and benefits will be apparentfrom the more detailed description of the invention.

ut the free radical catalyzed reaction of hydrogen sulfidewith ahydrocarbon having an ance with the Markownikofi rule, i. e. normaladdition m which the sulfhydryl radical attaches to the unsaturated100-2500 p. s. i. g.) the extent of conversion is increased and betteryields of primary mercaptan are obtained than if no water were present.Another source of free radicals are those induced by subjecting thereactants to ultraviolet radiations of below about 3,000 Angstrom units,e. g. 2,900 Angstrom units at temperatures of from about 0 5 to about 25C. U. S. 2,398,479 describes a process using ultraviolet rays of thedefined wave length for the free radical catalyzed reaction of hydrogensulfide with olefinic hydrocarbons. It must, of course, be rememberedthat in all instances the invention employs liquid water in the reactionzone and therefore temperatures above the freezing point of the watermust be used.

The hydrogen sulfide used is preferably high purity hydrogen sulfide andshould be free of'compounds which inhibit the chain reaction mechanismwhich occurs in free radical catalysis. Oxygen should be excluded fromthe system. Impure byproduct hydrogen sulfide streams (e.'g. thebyproduct hydrogen sulfide streams produced from Girbitol units oftenemployed by petroleum refiners and which may contain 15 or 20% ofcontaminants such as hydrocarbon gases, hydrogen, water vapor, etc. andwhich water vapor may constitute a portion or all of the water primarymercaptan, viz. the

needed in the practice of this invention) may be used provided they arefree of materials which inhibit or stop the free radical mechanism. Tomaximize the formation of mercaptans and minimize the formation ofthioethers, ratios of hydrogen sulfide to hydrocarbon of at least one orgreater, e. g. 1-10 mols H s/mol of hydrocarbon should be used, thehigher the mol ratio the higher is the molar ratio of mercaptan tothioether in the product.

In carrying out the invention, a hydrocarbon which has an olefiniclinkage is used. It may contain'one Or more olefinic linkages, thus, forexample, it may be 1,3-butadiene, isoprene, etc. It must contain anolefinic linkage in an aliphatic or cycloaliphatic grouping as distinctfrom the unsaturated linkage in an aromatic molecule such as benzene.The carbon atoms having the olefinic linkage may have attached theretoan alkyl, cycloalkyl, aryl, or other hydrocarbon substituent. Theinvention is particularly useful for manufacturing primary mercaptansfrom those hydrocarbons which have their olefinic linkage at a terminalcarbon atom, e. alpha-olefins. For example, aliphatic olefins such asstraight chain alpha-olefins having from 2 to 20 carbon atoms can beconverted in high yields to straightchain primary mercaptans. Thus,ethylene, propylene, butene-l, pentene-l, hexene-l, octene- 1,dodecene-l, hexadecene-l, etc. can be converted to their correspondingprimary mercaptans. It is not essential, however, that the hydrocarbonemployed be one which has an olefinic linkage at a terminal carbon atom.The olefinic linkage may be present within the hydrocarbon chain, suchas in butene-2, hexene-3, cyclohexene, or in other secondary olefins. Ashas been indicated, the carbon atom to which the olefinic linkage isattached may have other hydrocarbon substituents attached thereto, e. g.isobutene, styrene, alpha-methyl styrene, etc. Olefins obtained from thesymbol process or similar processes in which carbon monoxide andhydrogen are converted usually over an iron catalyst to a mixture ofolefins and chemicals may suitably be. employed after removal ofoxygenated compounds therefrom.

The reaction is carried out in the presence of a promoter which consistsof water. Distilled water, tap water or potable water can be used.Amounts such as 0.01 mol of water per mol of hydrocarbon can beemployed, and the amounts may be as much as 10 mols of water per mol ofhydrocarbon or greater if desired. Excellent results are obtained whenthe promoter water is employed in the amount of about 0.1 to 1 mol permol of hydrocarbon. The manner in which the water functions is unknown.It has the repeatedly demonstrated advantage of increasing the extent ofconversion of the hydrocarbon to a sulfur-containing product and alsoaffects the direction of the reaction, i. c. it causes the formation ofgreater amounts of mercaptan and reduces the yields of sulfide. For thelatter reason it increases the selectivity of the reaction to produceprimary mercaptans from alpha-olefins rather than producing largeamounts of organic sulfides therefrom. The use of water as the promoteris highly beneficial when the reaction is carried out in a ferrous metalreactor such as a carbon steel reactor or a stainless steel reactorparticularly those which are not new reactors or which havenot beenpassivated with nitric acid or similar materials to reduce the attack ofacids upon the metal. i

The pH of the water also has an effect upon the action of the waterpromoter. When acidic water is used, it produces a greater degree ofconversion than if basic water were employed. Thus, water having a pH ofless than 7, e. g. a pH of 1-3 may advantageously be employed, althougheven higher concentrations of hydrogen ions in the water may be present.

A number of experiments were carried out which demonstrate thepromotional effect upon the reaction when water is present in thereaction zone. The experimental procedure followed consisted of flushingthe stainless steel bomb with an inert gas to free it of oxygen,evacuating the bomb, introducing the free radical initiating agent intoticular runs) followed by introducing the olefin and then the hydrogensulfide into the bomb reactor. Thereafter the bomb was heated to thereactant temperature, viz. 90 C. when the catalyst wasalpha-alpha'-azodiisobutyronitrile and 120 C. when di-tertiarybutylperoxide was employed, fora reaction time of 18 hours. Sufiicientpressure was employed to maintain H 5 and olefin in the liquid phase, e.g. approximately 1,200 p. s. i. g. when propylene was employed. Theresults obtained with respect to formation of mercaptan and sulfide areshown in Table I which follows:

, the bomb (and water when it was employed in the pari Table I Run N0 "l1 l 2 l 3 1 4 Charge (mols): 1 i

Propene 6.2 6.5 Hexene-l 2. 98 2. 98 H l1. 2 2. 7S

Alpha,alpha -azodiisobutyron.1

Di-tertiarybutyl peroxide H Yields Mercnptan 12.7 31.4 26 43 Sulfide 8.013.2 as 20 Mercaptan/Sulfide Ratio 3.2l Ml .75 2.1

1 M 01 percent based on hydrocarbon charge.

The increase in the yield of products and the improvement in themercaptan/organic sulfide ratio which are caused by employing water as apromoter for the reaction are obvious from the above data.

Another series of runs was carried out in the same manner as waspreviously described, but employing varying amounts of water in thereaction Zone. Di-tertiarybutyl peroxide was employed as the freeradical initiating catalyst in the amount of 0.068 mol, a reaction timeof 18 hoursand a reaction temperature of approximately l15-120 C. wasused. The results obtained follow in Table II:

Table II Run No "i Charge (mols) Propane Yields LPropanethiol. .4Di-n-propyl Sulfide 1 Mcrcaptan/Sulfide Ratio 06 1 Mol percent based onG3chargc.

Similar advantages have been obtained when approximately 0.08 mol ofwater per mol of hydrocarbon and less were employed in the reactionzone.

In other series of runs, which were carried out in the manner previouslydescribed, the pH of the water was varied. In these experimentsapproximately 0.015 mol of di-tertiarybutyl peroxide was employed. Areaction temperature of approximately 115 C., a reaction time of about18 hours, and a final reaction pressure of approximately 1,000 p. s. i.g. were used. In run No. 10 the initial pH was 12.2 and was obtained byadding Na S to the water. In run No. 11 the initial pH of the water was1.1 which was achieved by adding HCl to the water. The results obtainedare shown in Table III which follows:

1 M01 percent based upon hydrocarbon charge.

It is evident from the above data that by maintaining a pH lower than 7and preferably a very high concentration of hydrogen ions in the water,a ctr-promotional effect between the water and the hydrogen ions on thereaction is observed. This co-promotional effect does not appear tochange the direction or selectivity of the reaction since essentiallythe same molar ratio of mercaptan to organic sulfide in the product isobserved.

Another series of runs was performed in which various 4. The process ofclaim 1 in which said water has a pH of less than 7.

5. The process of claim 1 in which said hydrocarbon has an olefiniclinkage at a terminal carbon atom.

6. The process of claim 1 in which said hydrocarbon is a straight chainalpha-olefin.

7. The process of claim 1 in which the reaction is carried out in aferrous metal reactor.

Table IV Run No 12 13 14 15 16 17 18 Hydrocarbon Propene Hexene-l Iso-Butene-2 a-Methyl Cyclo- Dodecbutene styrene hexene ene-1 Charge (mols):

Hydrocarbon 5. 1 2. 98 2. 72 2. 72 1. 95 1. 82 59 S 16.1 11.2 12. 4 11.913.1 15. 4 12.1 Water 2. 78 2. 78 2. 78 2. 78 2. 78 2. 78 2. 78Dl-tert-butyl Peroxide 013 .013 .013 .013 013 .021 .02 Yields 1Mercaptan 56 52 62 17 29 67 Sulfide 18 24 8 3 2 19 Mercaptan/Sulfideratio 3. 1 2. 2 7. 8 5. 7 14. 5 3. 5

1 Mol percent based on hydrocarbon charge.

It is evident from the above results that excellent conversion of theolefinic compound to its corresponding mercaptan, together with someyield of organic sulfide, is obtained.

While the invention has been described in connection with exampleswherein the olefinic linkage between the carbon atoms is present in ahydrocarbon, it is apparent that other functional groups may also bepresent in the hydrocarbon, and that compounds such as acrylonitrile,vinyl acetate and the like can advantageously be converted to theircorresponding mercaptans by means of this invention. These and othermodifications will be apparent from the described invention to thoseskilled in this art.

We claim:

1. In the free radical catalyzed reaction of hydrogen sulfide with ahydrocarbon having an olefinic linkage, the improvement which compriseseffecting said reaction in the presence of water in an amount sufiicientto promote the reaction.

2. The process of claim 1 in which said water is present in an amountbetween about 0.1 to 1 mol per mol of said hydrocarbon.

3. The process of claim 1 in which said water is present I in an amountbetween about 0.1 and 1 mol per mol of said hydrocarbon.

8. In the process of preparing primary mercaptans wherein hydrogensulfide is contacted with a hydrocarbon having an olefinic linkage atits terminal carbon atom in the presence of a free radical catalyticagent for said reac tion under conditions to cause addition of thehydrogen sulfide across the olefinic linkage, said hydrogen sulfidebeing employed in an amount in excess of one mol per mol of hydrocarbon,the improvement which comprises effecting said contacting in thepresence of a promotional amount of water for the reaction consisting ofbetween about .01 to 1 mol of water per mol of said hydrocarbon.

9. The process of claim 8 wherein the free radical catalytic agent isdi-tertiarybutyl peroxide.

10. The process of claim 8 wherein the free radical initiating agent isalpha-alpha'-azodiisobutyronitrile.

References Cited in the file of this patent UNITED STATES PATENTS2,522,512 Harman et al Sept. 19, 1950 2,522,590 Vaughan et al. Sept. 19,1950 FOREIGN PATENTS 462,856 Canada Jan. 31, 1950 UNITED STATES PATENToFEIcE QETIFICATE OF 'CGRECTION Patent No, 2,865,965 December 23, 1958Paul D. May et el.

Column 1, line 54, for "places" read place column 5, line 44, for"between about 0.1 to 1 mol" read mm of at least about 0001 mole Signedand sealed this 14th day of April 1959.,

SEAL) Attest:

KARL H,a AXLINE ROBERT C. WATSON Attesting Officer Commissioner ofPatents

1. IN THE FREE RADICAL CATALYZED FEACTION OF HYDROGEN SULFIDE WITH AHYDROCARBON HAVING AN OLEFINIC LINKAGE, THE IMPROVEMENT WHICH COMPRISESEFFECTING SAID REACTION IN THE PRESENCE OF WATER IN AN AMOUNT SUFFICIENTTO PROMOTE THE REACTION.